US11855730B2 - Apparatus and method for reconstructing downlink channel in wireless communication system - Google Patents
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Definitions
- the disclosure was made by or on behalf of the below listed parties to a joint research agreement.
- the joint research agreement was in effect on or before the date the disclosure was made and the disclosure was made as a result of activities undertaken within the scope of the joint research agreement.
- the parties to the joint research agreement are 1) Samsung Electronics Co., Ltd., and 2) KOREA ADVANCED INSTITUTE OF SCIENCE AND TECHNOLOGY.
- the disclosure relates to a wireless communication system. More particularly, the disclosure relates to an apparatus and a method for reconstructing a downlink channel in a wireless communication system.
- the 5G or pre-5G communication system is also called a “beyond 4G network” communication system or a “post long term evolution (post LTE)” system.
- FQAM frequency shift keying and quadrature amplitude modulation
- SWSC sliding window superposition coding
- ACM advanced coding modulation
- FBMC filter bank multi carrier
- NOMA non-orthogonal multiple access
- SCMA sparse code multiple access
- massive multiple-input multiple-output (massive MIMO) systems which use a large number of antennas for transmitters and receivers are considered as one of critical technologies in future wireless communication systems, and there has been extensive research regarding the same.
- CSI channel state information
- Another aspect of the disclosure is to provide an apparatus and a method for acquiring channel state information (CSI) by using an antenna sub-array in a wireless communication system.
- CSI channel state information
- Another aspect of the disclosure is to provide an apparatus and a method for acquiring channel state information for spatial multiplexing in a wireless communication system.
- An apparatus and a method according to various embodiments of the disclosure may improve the performance of a communication system through spatial multiplexing.
- FIG. 2 illustrates a configuration of a base station in a wireless communication system according to an embodiment of the disclosure
- FIG. 3 illustrates a configuration of a terminal in a wireless communication system according to an embodiment of the disclosure
- FIG. 4 illustrates a configuration of a communication unit in a wireless communication system according to an embodiment of the disclosure
- FIG. 5 illustrates a functional configuration for interaction between a base station and a terminal in a wireless communication system according to an embodiment of the disclosure
- FIG. 6 illustrates an example of an antenna structure of a base station in a wireless communication system according to an embodiment of the disclosure
- FIG. 7 illustrates an example of transmitting a reference signal (RS) from a base station to a terminal in a wireless communication system according to an embodiment of the disclosure
- FIG. 8 illustrates a flowchart for obtaining channel information in a wireless communication system according to an embodiment of the disclosure
- FIG. 9 illustrates a flowchart for reconstructing channel information using a ratio between channel sizes in a wireless communication system according to an embodiment of the disclosure
- FIG. 10 illustrates a flowchart for reconstructing channel information using angle of arrival (AoA) and angle of departure (AoD) in a wireless communication system according to an embodiment of the disclosure
- a physical channel and a signal may be used interchangeably with data or a control signal.
- the physical downlink shared channel (PDSCH) is a term referring to a physical channel through which data is transmitted, but the PDSCH may also be used to refer to data. That is, in the disclosure, the expression ‘transmitting a physical channel’ may be interpreted equally to the expression ‘transmitting data or signals through a physical channel’.
- the disclosure describes various embodiments using terms used in some communication standards (e.g., 3rd generation partnership project (3GPP)), but this is only an example for description.
- 3GPP 3rd generation partnership project
- Various embodiments of the disclosure may be easily modified and applied in other communication systems.
- FIG. 1 illustrates a wireless communication system according to an embodiment of the disclosure.
- FIG. 1 illustrates a base station 110 , a terminal 120 , and a terminal 130 as part of nodes using a wireless channel in a wireless communication system.
- FIG. 1 illustrates only one base station, but may further include another base station that is the same as or similar to the base station 110 .
- the base station 110 is a network infrastructure that provides wireless access to terminals 120 and 130 .
- the base station 110 has coverage defined as a predetermined geographic area based on a distance capable of transmitting a signal.
- the base station 110 may be referred to as an ‘access point (AP)’, an ‘eNodeB (eNB)’, ‘5th generation node (5G node), ‘next generation nodeB (gNB), ‘wireless point’, ‘transmission/reception point (TRP)’, or other terms having a technical meaning equivalent thereto.
- AP access point
- eNB evolved node
- 5G node 5th generation node
- gNB next generation nodeB
- TRP transmission/reception point
- Each of the terminal 120 and the terminal 130 is a device used by a user, and performs communication with the base station 110 through a wireless channel. In some cases, at least one of the terminal 120 and the terminal 130 may be operated without the user's involvement. That is, at least one of the terminal 120 and the terminal 130 is a device that performs machine type communication (MTC) and may not be carried by a user.
- MTC machine type communication
- Each of the terminal 120 and the terminal 130 may be referred to as ‘user equipment (UE)’, ‘mobile station’, ‘subscriber station’, ‘remote terminal’, ‘wireless terminal’, ‘user device’, or other terms having an equivalent technical meaning thereto in addition to terminal.
- the base station 110 , the terminal 120 , and the terminal 130 may transmit and receive wireless signals in millimeter wave (mmWave) bands (e.g., 28 GHz, 30 GHz, 38 GHz, and 60 GHz).
- mmWave millimeter wave
- the base station 110 , the terminal 120 , and the terminal 130 may perform beamforming.
- the beamforming may include transmission beamforming and reception beamforming. That is, the base station 110 , the terminal 120 , and the terminal 130 may assign directivity to a transmission signal or a reception signal.
- the base station 110 and the terminals 120 and 130 may select serving beams 112 , 113 , 121 , and 131 through a beam search or beam management procedure.
- subsequent communication may be performed through a resource having a quasi co-located (QCL) relationship with the resource transmitting the serving beams 112 , 113 , 121 , and 131 .
- QCL quasi co-located
- the first antenna port and the second antenna port may be evaluated to be in a QCL relationship.
- the large-scale characteristics may include at least one of delay spread, Doppler spread, Doppler shift, average gain, average delay, and a spatial receiver parameter.
- FIG. 2 illustrates a configuration of a base station in a wireless communication system according to an embodiment of the disclosure.
- the configuration illustrated in FIG. 2 may be understood as a configuration of the base station 110 .
- Terms such as “ . . . unit” and “-er” used below refer to units that process at least one function or operation, and may be implemented by hardware, software, or a combination of hardware and software.
- the base station includes a wireless communication unit 210 , a backhaul communication unit 220 , a storage unit 230 , and a control unit 240 .
- the wireless communication unit 210 may be composed of a digital unit and an analog unit, and the analog unit may be composed of a plurality of sub-units according to operating power, operating frequency, and the like.
- the digital unit may be implemented as at least one processor (e.g., a digital signal processor (DSP)).
- DSP digital signal processor
- the storage unit 230 stores data such as a basic program, an application program, and configuration information for the operation of the base station.
- the storage unit 230 may be configured as a volatile memory, a nonvolatile memory, or a combination of a volatile memory and a nonvolatile memory.
- the storage unit 230 provides stored data according to a request by the control unit 240 .
- the communication unit 310 may perform functions for transmitting and receiving signals through a wireless channel.
- the communication unit 310 may perform a conversion function between a baseband signal and a bit string according to a physical layer standard of a system.
- the communication unit 310 when transmitting data, the communication unit 310 generates complex symbols by encoding and modulating a transmission bit string.
- the communication unit 310 reconstructs the received bit string through demodulation and decoding of the baseband signal.
- the communication unit 310 up-converts the baseband signal into an RF band signal and transmits the RF band signal through an antenna, and down-converts the RF band signal received through the antenna into a baseband signal.
- the communication unit 310 may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, and the like.
- the storage unit 320 stores data such as a basic program, an application program, and configuration information for the operation of the terminal.
- the storage unit 320 may be configured as a volatile memory, a nonvolatile memory, or a combination of a volatile memory and a nonvolatile memory.
- the storage unit 320 provides stored data according to a request from the control unit 330 .
- the control unit 330 controls overall operations of the terminal. For example, the control unit 330 transmits and receives signals through the communication unit 310 . In addition, the control unit 330 writes and reads data in the storage unit 320 . In addition, the control unit 330 may perform functions of a protocol stack required by the communication standard. To this end, the control unit 330 may include at least one processor or a micro-processor, or may be a part of the processor. In addition, a part of the communication unit 310 and the control unit 330 may be referred to as a communication processor (CP). According to various embodiments, the control unit 330 may control a terminal to perform operations according to various embodiments to be described later.
- CP communication processor
- FIG. 4 illustrates a configuration of a communication unit in a wireless communication system according to an embodiment of the disclosure.
- FIG. 4 illustrates an example of a detailed configuration of the wireless communication unit 210 of FIG. 2 or the communication unit 310 of FIG. 3 .
- FIG. 4 illustrates components for performing beamforming as a part of the wireless communication unit 210 of FIG. 2 or the communication unit 310 of FIG. 3 .
- the digital beamforming unit 404 performs beamforming on a digital signal (e.g., modulation symbols). To this end, the digital beamforming unit 404 multiplies the modulation symbols by beamforming weights.
- the beamforming weights are used to change the magnitude and phase of a signal, and may be referred to as a precoding matrix, a pre-coder, or the like.
- the digital beamforming unit 404 outputs the digital beamformed modulation symbols to the plurality of transmission paths 406 - 1 to 406 -N.
- modulation symbols may be multiplexed or the same modulation symbols may be provided to a plurality of transmission paths 406 - 1 to 406 -N.
- CSI channel state information
- TDD time division duplexing
- FIG. 5 illustrates a functional configuration for interaction between a base station and a terminal in a wireless communication system according to an embodiment of the disclosure.
- FIG. 5 exemplifies functional components of the base station 110 and the terminal 120 , and the components illustrated in FIG. 5 may be included in at least one of the components described with reference to FIG. 2 or 3 .
- downlink RSs (e.g., CSI-RSs) are generated by the RS generator 502 in the base station 110 .
- the downlink RS is beamformed by an RS beamformer 504 , and then transmitted through K antenna ports 506 - 1 to 506 -K configured from N BS antennas.
- Downlink RSs transmitted through the K antenna ports 506 - 1 to 506 -K are received by antennas (e.g., M UE antennas) of the terminal 120 through channels.
- the transceiver 508 Based on the downlink RSs received by the antennas of the terminal 120 , the transceiver 508 infers channel information (e.g., h CSI-RS-uq ) between the antenna ports 506 - 1 to 506 -K of the base station 110 and the antennas of the terminal 120 , and the inferred channel information is quantized by the quantization unit 510 .
- the quantized channel information (e.g., H CSI-RS ) is fed back to the base station 110 .
- the transceiver 508 transmits an uplink RS (e.g., SRS) through one of the plurality of antennas.
- the base station 110 receives the uplink signals including uplink RS through the antenna ports 506 - 1 to 506 -K.
- the channel reconstructor 514 of the base station 110 reconstructs more accurate channel information using the first channel information (e.g., h SRS ) inferred based on the uplink RS and the second channel information (e.g., H CSI-RS ) fed back from the terminal 120 .
- the reconstructed channel information is more accurate than the first channel information or the second channel information.
- the first channel information is channel information for one of the antennas of the terminal 120
- the reconstructed channel information may be more intact in terms of quantity.
- the second channel information is quantized channel information
- the reconstructed channel information may be more accurate in terms of quality.
- a T , A H , and A + represent transpose, conjugate transpose, and pseudo-inverse of matrix A.
- A(:,m:n) is a submatrix consisting of the mth column to the nth column of matrix A
- A(m:n,;) is a submatrix consisting of the mth row to the nth row of the matrix A.
- a(m:n) is a vector consisting of the mth to nth elements of vector a.
- represents an absolute value of the complex number
- ⁇ represents an l′ 2 norm of the vector and ⁇ F represents a Frobenius norm of the matrix.
- 0 m denotes an all zero vector of m ⁇ 1, and I m denotes an identity matrix of m ⁇ m.
- FIG. 6 illustrates an example of an antenna structure of a base station in a wireless communication system according to an embodiment of the disclosure.
- FIG. 6 illustrates a UPA.
- the number of antenna ports or antennas may be expressed as variables J and K if the base station operates the ULA, and variables Nver and Nhor if the UPA is operated.
- the CSI-RS known to both the terminal and the base station is transmitted from the base station to the terminal through each antenna port.
- the terminal 120 may receive K reference signals, quantize channel information inferred from the received reference signals, select one codeword from a precoding matrix indicator (PMI) codebook, and transmit index of the selected codeword to the base station.
- PMI precoding matrix indicator
- y k H H p k x k Equation 1
- Equation 1 y k represents a received signal corresponding to a signal transmitted through the k-th antenna port, H H represents a channel between a base station and a terminal of N BS ⁇ M UE size, p k represents a beamforming vector corresponding to the k-th antenna port, and x k represents a signal transmitted through the k-th antenna port.
- p k [0 (k-1)J T ,w k T ,0 N BS -kJ T ] T Equation 2
- Equation 2 p k represents a beamforming vector corresponding to the k-th antenna port, and w k represents a beamforming weight vector applied to the k-th antenna sub-array.
- the terminal configures an unquantized effective CSI-RS channel matrix H CSI-RS-uq based on K reception signals.
- the unquantized effective channel matrix may be expressed as Equation 3.
- H CSI-RS-uq represents an unquantized effective channel matrix
- yk represents a k-th column of the effective channel matrix
- H H represents a downlink channel
- P represents a precoding matrix
- H CSI-RS-uq is a matrix of M UE ⁇ K size
- H H CSI-RS is a matrix of L ⁇ K size.
- the base station may recognize L max , which is the maximum number of feedback layers of the terminal, rather than the number of antennas M UE in the terminal, and L is less than or equal to L max .
- the base station may infer the downlink channel from the uplink SRS transmitted from the terminal by utilizing the channel reciprocity between the downlink and the uplink.
- the base station may infer a vector h H SRS of 1 ⁇ N BS size corresponding to one of the rows of H H without considering noise.
- FIG. 8 illustrates a flowchart 800 for obtaining channel information in a wireless communication system according to an embodiment of the disclosure.
- FIG. 8 illustrates an operating method of the base station 110 .
- the base station transmits downlink RSs to the terminal.
- the base station transmits downlink RSs through a plurality of antenna ports.
- one antenna port may correspond to one antenna sub-array.
- the base station may perform precoding, that is, beamforming, on downlink RSs.
- the base station infers a second channel matrix based on at least one uplink RS.
- the second channel matrix indicates channel information between one antenna used for transmitting at least one uplink RS and antenna ports of the base station.
- the base station reconstructs channel information to be used for data transmission based on the first channel matrix and the second channel matrix.
- the base station reconstructs channel information between the antenna ports of the base station and the antennas of the terminal based on the quantized channel information fed back from the terminal and the partial channel information inferred by the base station.
- the base station may reconstruct channel information based on a ratio of channel values corresponding to the antennas of the terminal or based on angle of arrival (AoA) and angle of departure (AoD) of the channel.
- AoA angle of arrival
- AoD angle of departure
- FIG. 9 illustrates a flowchart for reconstructing channel information using a ratio between channel sizes in a wireless communication system according to an embodiment of the disclosure.
- FIG. 9 illustrates an operating method of the base station 110 .
- the base station identifies an antenna that has transmitted at least one uplink RS.
- the antenna that has transmitted at least one uplink RS may be identified based on a second channel matrix inferred using at least one uplink RS.
- the antenna that has transmitted at least one uplink RS may be treated as a predefined antenna.
- the base station determines ratios of channel values between antennas of the terminal based on the first channel matrix.
- the base station may determine ratios of channel sizes between antennas of the terminal based on the quantized channel information.
- the base station may determine a ratio of channel sizes between the first antenna of the terminal and the second antenna of the terminal.
- the ratios may include relative sizes of the remaining antennas with respect to the antenna identified as having transmitted the uplink RS.
- the base station reconstructs channel information from the second channel matrix based on the ratios of the channel values.
- the base station may determine columns or rows of channel information corresponding to other antennas from the second channel matrix based on the ratio values. Accordingly, the base station may reconstruct channel information between the antenna ports of the base station and the antennas of the terminal.
- the base station may reconstruct channel information based on ratios of channel values between the antennas of the terminal. More specifically, a process of reconstructing channel information based on ratios of channel values will be described with reference to the following equations. In the following description, a method for reconstructing channel information based on ratios of channel values may be referred to as a ‘ratio method’.
- H CSI-RS-uq of Equation 3 may be expressed as Equation 4 below.
- H CSI - RS - uq [ h 1 H ⁇ p 1 h 1 H ⁇ p 2 ... h 1 H ⁇ P K h 2 H ⁇ p 1 h 2 H ⁇ p 2 h 2 H ⁇ p K ⁇ ⁇ ⁇ ⁇ h M UE H ⁇ p 1 h M UE H ⁇ p 2 ... h M UE H ⁇ p K ] Equation ⁇ 4
- H CSI-RS-uq represents an unquantized effective channel matrix
- h m represents a channel vector between the base station and the m-th antenna of the terminal
- p k represents a beamforming vector corresponding to the k-th antenna port
- M UE represents the number of antennas of the terminal.
- FIG. 10 illustrates a flowchart 1000 for reconstructing channel information using angle of arrival (AoA) and angle of departure (AoD) in a wireless communication system according to an embodiment of the disclosure.
- FIG. 10 illustrates an operating method of the base station 110 .
- the base station may reconstruct channel information based on the AoA value and the AoD value. More specifically, the process of reconstructing channel information based on the AoA value and the AoD value will be described with reference to the following equations. In the following description, a method for reconstructing channel information based on the AoA value and the AoD value may be referred to as a ‘pre-search method’.
- ⁇ pre represents the downlink channel modeled for the pre-search method
- T AoA represents the number of dominant AoAs
- T AoD represents the number of dominant AoDs
- u represents the index of AoA
- v represents the index of AoD
- ⁇ circumflex over ( ⁇ ) ⁇ u represents the u-th AoA
- ⁇ circumflex over ( ⁇ ) ⁇ v represents the v-th AoD
- c u,v represents the complex path gain of the path composed of AoA ⁇ circumflex over ( ⁇ ) ⁇ u and AoD ⁇ circumflex over ( ⁇ ) ⁇ v
- a AoA ( ⁇ circumflex over ( ⁇ ) ⁇ u ) represents the array response vector in the terminal corresponding to AoA( ⁇ circumflex over ( ⁇ ) ⁇ u )
- a AoD ( ⁇ circumflex over ( ⁇ ) ⁇ v ) represents the array response vector in the base station corresponding to AoD( ⁇ circumflex over ( ⁇
- Equation 8 a AoD ( ⁇ circumflex over ( ⁇ ) ⁇ v ) represents an array response vector in the base station, N BS represents the number antennas of the base station, and ⁇ circumflex over ( ⁇ ) ⁇ v represents the v-th AoD.
- Equation 8 When the base station operates a uniform planar array (UPA), the array response vector of Equation 8 may be expressed as Equation 9 below.
- the base station first searches for dominant AoAs and AoDs.
- ⁇ r ( ⁇ i ) the signal strength for the i-th angle
- a AoA ⁇ circumflex over ( ⁇ ) ⁇ i
- H CSI-RS represents the quantized channel information fed back from the terminal.
- ⁇ /R ULA represents a resolution for
- i has values of 1, 2, . . . , R ULA +1.
- Equation 14 ⁇ i represents the i-th angle, ⁇ /R ULA represents a resolution for ⁇ i .
- i has values of 1, 2, . . . , R ULA +1.
- Equation 15 the signal strength corresponding to the vertical angle ⁇ l ver and the horizontal angle ⁇ l hor may be modeled as Equation 15 and Equation 16 below.
- ⁇ t ( ⁇ l ver , ⁇ l hor )
- a AoA represents the AoA value
- a AoA ( ⁇ circumflex over ( ⁇ ) ⁇ u ) represents the array response vector from the terminal.
- Equation 18 the matrix A AoD of N BS ⁇ T AoD size may be expressed as Equation 18 below when the base station operates ULA, and may be expressed as Equation 19 below when the base station operates UPA.
- a AoD [a AoD ( ⁇ circumflex over ( ⁇ ) ⁇ 1 ), a AoD ( ⁇ circumflex over ( ⁇ ) ⁇ 2 ), . . . , a AoD ( ⁇ circumflex over ( ⁇ ) ⁇ T AoD )] Equation 18
- a AoD represents the AoD value
- a AoD ( ⁇ circumflex over ( ⁇ ) ⁇ v ) represents the array response vector from the base station.
- a AoD [a AoD ( ⁇ circumflex over ( ⁇ ) ⁇ 1,ver , ⁇ circumflex over ( ⁇ ) ⁇ 2,hor ), a AoD ( ⁇ circumflex over ( ⁇ ) ⁇ 2,ver , ⁇ circumflex over ( ⁇ ) ⁇ 2,hor ), . . . , a AoD ( ⁇ circumflex over ( ⁇ ) ⁇ T AoD ,ver , ⁇ circumflex over ( ⁇ ) ⁇ T AoD ,hor )] Equation 19
- a AoD represents the AoD value
- a AoD ( ⁇ circumflex over ( ⁇ ) ⁇ v,ver , ⁇ circumflex over ( ⁇ ) ⁇ v,hor ) represents the array response vector from the base station.
- C ⁇ pre argmin C ⁇ 1 ⁇ C T AoA ⁇ T AoD ⁇ ⁇ A AoA ⁇ C ⁇ 1 ⁇ A AoD H ⁇ P - H CSI - RS H ⁇ F + ⁇ ⁇ ⁇ A AoA ⁇ C ⁇ 1 ⁇ A AoD H ( : , m Tx ) - h SRS ⁇ Equation ⁇ 20
- Equation 20 ⁇ pre represents the optimal path gain vector, T AoA represents the number of dominant AoAs, T AoD represents the number of dominant AoDs, A AoA represents the AoA value, ⁇ 1 represents the candidate value of the optimal path gain vector, P represents the precoding matrix, A AoD represents the AoD value, H CSI-RS represents a quantized channel matrix fed back from the terminal, m TX represents the index of the antenna used to transmit the uplink RS from the terminal, h SRS represents a channel matrix inferred using uplink RS, and ⁇ represents a regularization factor having a positive real value, and as ⁇ is larger, a greater weight is given to reduce the difference between the m TX -th row of reconstructed channel information and the h SRS .
- Equation 21 The downlink channel reconstructed through the pre-search method may be expressed as Equation 21 below.
- ⁇ pre H A AoA ⁇ pre A AoD H Equation 21
- Equation 21 ⁇ pre H represents the downlink channel reconstructed through the pre-search method, A AoA represents the AoA value, ⁇ pre represents the optimal path gain vector, and A AoD represents the AoD value.
- Equation 22 ⁇ pre H (m TX ,:) represents the m TX -th row of ⁇ pre H , and h SRS represents a channel matrix inferred using an uplink RS.
- H CSI-RS-uq represents an unquantized valid channel matrix
- a AoA represents an AoA value
- C 2 represents a path gain vector
- a AoD represents an AoD value
- P represents a precoding matrix
- Equation ⁇ pinv represents a channel matrix inferred by the pseudo-inverse method
- a AoA represents an AoA value
- ⁇ pinv represents a path gain vector determined by pseudo-inverse
- a AoD represents an AoD value.
- channel information may be reconstructed.
- reconstructing channel information an operation of identifying an antenna of a terminal used to transmit an uplink RS, for example, SRS is performed.
- the antenna of the terminal used to transmit the SRS may be determined based on the second channel matrix and the first channel matrix. Due to channel reciprocity between downlink and uplink, the m TX -th row of h H SRS and downlink channel H H indicate information on the same channel. Therefore, it is expected that h H SRS is most similar to the m TX -th row of H CSI-RS-uq . Based on this, the base station may identify the most similar row to the first channel matrix among the rows included in the first channel matrix, and determine the antenna corresponding to the identified row as the antenna of the terminal used to transmit the SRS. The similarity of the rows may be determined based on an error value or a dot product value. The method using the error value is expressed as Equation 26 below, and the method using the dot product value is expressed as Equation 27 below.
- Equation 26 ⁇ circumflex over (m) ⁇ Tx represents an antenna index inferred to be used to transmit uplink RS, H CSI-RS represents a quantized channel matrix fed back from the terminal, h SRS represents a channel matrix inferred using uplink RS, and P represents a precoding matrix.
- the number of antenna ports of the base station is set to 4 and the regularization factor ⁇ was set to 10, and the number of dominant AoAs and AoDs, T AoA and T AoD are set to L and 4, R ULA is set to 3600, R UPA,ver is set to 200, and R UPA,hor is set to 200.
- Equation 30 ⁇ H represents the Hermitian of the inferred downlink channel, ⁇ represents the left-singular vector obtained by the singular value decomposition (SVD), ⁇ circumflex over ( ⁇ ) ⁇ represents a diagonal matrix containing singular values, and ⁇ circumflex over (V) ⁇ represents a right-singular vector obtained by singular value decomposition.
- F ⁇ circumflex over (V) ⁇ (:,1: L max ) Equation 31
- FIGS. 11 to 14 illustrate performance graphs of a wireless communication system according to various embodiments of the disclosure.
- ‘CSI-RS’ is a case in which F in Equation 31 is set to P ⁇ circumflex over (V) ⁇ CSI-RS , and corresponds to a baseline in which downlink channel reconstruction is not performed.
- ⁇ circumflex over (V) ⁇ CSI-RS corresponds to a right singular matrix when H CSI-RS is decomposed into singular values as Equation 30.
- FIG. 11 illustrates a cumulative density function (CDF) of a rate when the base station operates a ULA according to an embodiment of the disclosure.
- CDF cumulative density function
- the indication may indicate quantized channel information between antenna ports of the base station and antennas of the terminal.
- the antenna used to transmit the at least one uplink RS may be identified as a predefined antenna or an antenna corresponding to a row most similar to the second channel information among rows of the first channel matrix.
- the channel information may be reconstructed by determining dominant AoAs included in the AoA value and dominant AoDs included in the AoD value, determining a channel matrix based on the AoA value and the AoD value by multiplying the AoA value, the AoD value, and a path gain value, and replacing one row of the channel matrix with the second channel matrix.
- the at least one processor may identify an antenna used to transmit the at least one uplink RS from the terminal.
- the channel information may be reconstructed by determining ratios of a channel size for another antenna compared to an antenna used for transmitting the at least one uplink RS based on the first channel matrix, and by determining rows of channel information corresponding to another antennas from the second channel matrix based on the ratios.
- the channel information may be reconstructed based on an angle of arrival (AoA) value and an angle of departure (AoD) value of a channel.
- AoA angle of arrival
- AoD angle of departure
Abstract
Description
y k =H H p k x k Equation 1
p k=[0(k-1)J T ,w k T,0N
Ĥ pre=Σu=1 T
χr(ψi)=∥a AoA h(ψi)H CSI-RS H∥
χr(ψi)≥χr(ψi+1),χr(ψi)≥χr(ψi−1) Equation 12
χt(μi)=|a AoD H(μi)h SRS| Equation 13
χt(μl
represent resolutions for μl
A AoA =[a AoA({circumflex over (ψ)}1),a AoA({circumflex over (ψ)}2), . . . a AoA({circumflex over (ψ)}T
TABLE 1 |
|
1: | Initialize OULA as an empty set |
2: | h ← hSRS |
3: | for υ = 1, 2, . . . , TAoD do |
4: | Initialize imax |
5: | for i = 1, 2, . . . , RULA do |
6: | Calculate χi t |
7: | end for |
8: |
|
9: | {circumflex over (μ)}υ ← μi |
10: | h ← h − (hHaAoD({circumflex over (μ)}υ))aAoD({circumflex over (μ)}υ) |
11: | OULA ← {circumflex over (μ)}υ |
12: | end for |
TABLE 2 |
|
1: | Initialize OUPA as an empty set |
2: | h ← hSRS |
3: | for υ = 1, 2, . . . , TAoD do |
4: | Initialize ver,max, hor,max |
5: | for ver = 1, 2, . . . , RUPA,ver do |
6: | for hor = 1, 2, . . . , RUPA,hor do |
7: | Calculate |
8: | end for |
9: | end for |
10: |
|
11: | {circumflex over (μ)}υ,ver ← |
12: | {circumflex over (μ)}υ,ver ← |
13: | h ← h − (hHaAoD({circumflex over (μ)}υ,ver, {circumflex over (μ)}υ,hor))aAoD({circumflex over (μ)}υ,ver, {circumflex over (μ)}υ,hor) |
14: | OUPA ← ({circumflex over (μ)}υ,ver, {circumflex over (μ)}υ,hor) |
15: | end for |
A AoD =[a AoD({circumflex over (μ)}1),a AoD({circumflex over (μ)}2), . . . ,a AoD({circumflex over (μ)}T
A AoD =[a AoD({circumflex over (μ)}1,ver,{circumflex over (μ)}2,hor),a AoD({circumflex over (μ)}2,ver,{circumflex over (μ)}2,hor), . . . ,a AoD({circumflex over (μ)}T
Ĥ pre H =A AoA Ĉ pre A AoD H Equation 21
Ĥ pre H(m Tx,:)=h SRS H Equation 22
H CSI-RS-uq ≈A AoA C 2 A AoD H P Equation 23
Ĉ pinv =A AoA † H CSI-RS H(A AoD H P)† Equation 24
Ĥ pinv =A AoA Ĉ pinv A AoD H Equation 25
Ĥ H =Û{circumflex over (Σ)}{circumflex over (V)} H
F={circumflex over (V)}(:,1:L max) Equation 31
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